1. Field of the Invention
The present invention relates to an image processing system for acquiring the spectral properties of a dye used to stain a specimen.
2. Description of the Related Art
One of the physical quantities expressing a physical property specific to a subject is transmittance. Transmittance is a physical quantity representing the ratio of transmitted light to incident light at each wavelength, and is information that is inherent to an object, having a value that is not affected by outside influences, unlike color information like the RGB value, which varies depending on changes in illumination light. Thus, transmittance is used in various fields of application as information for reproducing the colors of the subjects itself. For example, biological tissue specimens, in particular in the field of pathological diagnosis using pathological specimens, transmittance is used in order to analyze a captured image of a specimen.
In pathological diagnosis, microscopes are used to observe an enlarged view in order to obtain various findings after a block specimen obtained by organ excision or a pathological specimen obtained by needle biopsy is sectioned to a thickness of several microns. Particularly, an observation based on transmittance by using an optical microscope has been one of the most commonly practiced observation methods because the equipments are relatively inexpensive and easy to handle, and because this method has historically been used for many years. Therein, because the thinly sliced specimen essentially neither absorbs nor scatters light and is thus nearly colorless and transparent, staining is generally performed by means of a dye prior to observation.
There have been various methods proposed for staining, the total thereof reaching more than 100 different types, but in particular concerning pathological specimens, the standard has been to use hematoxylin-eosin staining (hereinafter called “H&E staining”), which uses two types of dyes, bluish-purple hematoxylin and red-colored eosin. Hematoxylin is a natural substance extracted from plants, and has no stainability itself. However, hematin, which is an oxide thereof, is a basophilic dye that binds to negatively charged substances. The deoxyribonucleic acid (DNA) contained within the cellular nucleus is negatively charged due to the phosphate groups contained as constituent elements, and therefore binds with hematin and is stained bluish-purple. Even though it is not hematoxylin but rather hematin, the oxide thereof, that possesses stainability, as mentioned above, hematoxylin is generally used to refer to the dye, and this convention is used herein. On the other hand, eosin is an acidophilic dye that binds to positively charged substances. Amino acids and proteins can be charged either positively or negatively depending on the pH environment, and have a strong tendency to be positively charged under acidity. For this reason, acetic acid is sometimes added when using eosin solution. The proteins contained in the cytoplasm are stained pink from red by binding with eosin. In a specimen after H&E staining (a stained specimen), cellular nucleic and bone tissues or the like are stained bluish purple, while the cytoplasm, connective tissue, erythrocytes and the like are stained red, thus becoming easily visible. As a result, the observer is able to ascertain the sizes, positional relationships or the like of the elements constituting the tissue, such as cellular nuclei, and can thus determine the morphological state of the specimen.
Observation of specimens is also carried out by performing multiband image capturing on the specimen for display on the display screen of an external device, in addition to visual inspection by an observer. When displaying on the display screen, then processing for estimating the transmittance at points on the specimen (sample points) from the captured multiband image, processing for estimating the amount of dye used to stain the specimen based on the estimated transmittance, processing for correcting the color of the image based on the estimated amount of dye and the like are performed, thus correcting the properties of the camera and variations in the staining conditions and so on, in order to synthesize a display image which is an RGB image for displaying the specimen. Appropriately estimating the amount of dye makes it possible to correct darkly stained specimens and lightly stained specimens to images having a coloring equivalent to that of a properly stained specimen.
Methods for estimating the transmittance of sample points from a multiband image of a specimen include, for example, an estimation method by principal component analysis (for example, see “Development of support systems for pathology using spectral transmittance—The quantification method of stain conditions,” Proceedings of SPIE, Vol. 4684, 2002, p. 1516-1523), or an estimation method by the Wiener estimation (for example, see “Color Correction of Pathological Images Based on Dye Amount Quantification,” OPTICAL REVIEW, Vol. 12, No. 4, 2005, p. 293-300). The Wiener estimation is widely known as a linear filtration technique for estimating an original signal from an observed signal on which noise has been superimposed, and is a method for minimizing error by taking into consideration the statistical properties of the object of observation and the properties of noise (observation noise). Because signals from cameras contain a certain amount of noise, the Wiener estimation is very useful as a method for estimating an original signal.
For example, the amount of dye in a specimen can be corrected by using a method such as the Wiener estimation to estimate the amount of dye in each pixel of a multiband image and then virtually adjusting the amount of dye at each corresponding sample point in order to synthesize an adjusted image of the specimen. At this point, automatic color normalization processing is performed, thus making it possible to adjust the amount of dye at each sample point to appropriate staining conditions. Preparing an appropriate user interface also makes it possible for a user to manually adjust the amount of dye. The display image that has been synthesized for display is, for example, displayed on the screen of a display device for use in pathological diagnosis and the like by a doctor and the like. Accordingly, even though a specimen has variations in stain, it is possible to observe the image that has been adjusted to appropriate staining conditions.
Also, small-scale medical facilities lacking staining equipment for specimens will often commission specimen staining to medical facilities that do have staining equipment. The display image is synthesized at the commissioned medical facility by staining the specimen for multiband image capturing, and then performing color normalization processing on the captured multiband image of the specimen. On the other hand, the data of the display image that has been synthesized at the commissioned medical facility is acquired at the commissioning medical facility via a predetermined network, in order to be used for pathological diagnosis and the like. When there is a desire to adjust the staining conditions (the amount of dye) in the display image, the commissioning medical facility again commissions synthesis of a display image from the commissioned medical facility for a second acquisition of the display image data, via the network, in which the amount of dye has been corrected.